The use of antibodies to the CD20 antigen as diagnostic and/or therapeutic agents for B-cell lymphoma has previously been reported. CD20 is a useful marker or target for B-cell lymphomas as this antigen is expressed at very high densities on the surface of malignant B-cells, i.e., B-cells wherein unabated proliferation can lead to B-cell lymphomas.
CD20 or Bp35 is a B-lymphocyte-restricted differentiation antigen that is expressed during early pre-B-cell development and remains until plasma cell differentiation. It is believed by some that the CD20 molecule may regulate a step in the B-cell activation process which is required for cell cycle initiation and differentiation. Moreover, as noted, CD20 is usually expressed at very high levels on neoplastic (“tumor”) B-cells. The CD20 antigen is appealing for targeted therapy, because it does not shed, modulate, or internalize.
Previous reported therapies involving anti-CD20 antibodies have involved the administration of a therapeutic anti-CD20 antibody either alone or in conjunction with a second radiolabeled anti-CD20 antibody, or a chemotherapeutic agent.
In fact, the Food and Drug Administration has approved the therapeutic use of one such anti-CD20 antibody, RITUXAN®, for use in relapsed and previously treated low-grade non-Hodgkin's lymphoma (NHL). Also, the use of RITUXAN® in combination with a radiolabeled murine anti-CD20 antibody has been suggested for the treatment of B-cell lymphoma.
However, while anti-CD20 antibodies and, in particular, RITUXAN® (U.S.; in Britain, MABTHERA®; in general Rituximab), have been reported to be effective for treatment of B-cell lymphomas, such as non-Hodgkin's lymphoma, the treated patients are often subject to disease relapse. Therefore, it would be beneficial if more effective treatment regimens could be developed. More specifically, it would be advantageous if anti-CD20 antibodies had a beneficial effect in combination with other lymphoma treatments, and if new combined therapeutic regimens could be developed to lessen the likelihood or frequency of relapse. Also, it would be helpful if current treatment protocols for B-cell lymphoma were improved whereby patients with lymphomas which are refractory to other treatment methods could be treated with chimeric or radiolabeled anti-CD20 antibodies. It would also be helpful if treatment with anti-CD20 antibodies, particularly in combination with other treatments, could be used as therapy for other types of lymphoma besides low grade, follicular non-Hodgkin's lymphoma (NHL).